1. Field of the Invention
The present invention relates to a swash-plate operated reciprocatory piston type compressor (hereinafter referred to as a swash plate type compressor) for use in air-conditioning systems for vehicles and, in particular, to an improved shoe and swash plate lubricator incorporated into a swash plate type compressor to supply sliding contact faces of a swash plate and shoes intervened between the swash plate and reciprocatory pistons with a required amount of lubricating oil during the operation of the compressor.
2. Description of the Related Art
A typical swash plate type compressor as disclosed in, for example, U.S. Pat. No. 3,801,227 to Nakayama and U.S. Pat. No. 3,955,899 to Nakayama et al., is provided with a pair of horizontal axially aligned front and rear cylinder blocks which form a combined cylinder block, and the combined cylinder block is closed at both ends by front and rear housings, via valve plates. The front and rear housings form refrigerant suction chambers and refrigerant discharge chambers, and inside the combined cylinder block are formed a plurality of cylinder bores arranged around a central axis of the combined cylinder block and having axes in parallel with the central axis. Each of the cylinder bores is interconnected to the suction and discharge chambers of the front and rear housings. The combined cylinder block also has a centrally longitudinal bore formed therein, and a drive shaft rotatably mounted therein, and a swash plate chamber in which a swash plate keyed on the drive shaft is rotatably received. The swash plate rotates with the drive shaft and is operatively engaged with double-headed pistons slidably fitted in the cylinder bores so as to reciprocate the pistons across the swash plate chamber. That is, shoes are arranged between the swash plate and the double-headed pistons to provide a universal coupling therebetween and to cause a reciprocatory compressing motion of the pistons within the cylinder bores in response to the rotation of the swash plate. The central portion of each of the double-headed pistons is provided with a recess through which the swash plate passes during the rotation thereof, and a pair of spherical sockets to receive the shoes. Each of the shoes has a circular flat face in sliding contact with the oblique face of the swash plate and a half-spherical face in sliding engagement with the socket of the associated piston.
With the above-mentioned swash plate type compressor, when the compressor is used for compressing a refrigerant gas of the air-conditioning system of a vehicle, a refrigerant gas containing a lubricating oil is introduced from the outside air-conditioning circuit into the suction chambers, via the swash plate chamber, and is discharged from the compressor toward the outside air-conditioning circuit after compression. The lubricating oil contained in the refrigerant gas lubricates the contacting faces of the shoes and the swash plate and respective sockets of the pistons when the oil enters the swash plate chamber. However, since the circular flat face of each shoe and the oblique face of the swash plate are in close contact, sometimes a sufficient amount of lubricating oil is not supplied to the contacting faces of the shoe and swash plate. Moreover, since the lubricating oil entering the swash plate chamber is subjected to centrifugal force by the rotating swash plate and is scattered radially outward within the swash plate, the lubricating oil cannot be retained between the shoes and the swash plate. Thus, a lack of lubrication for the swash plate and the shoes engaged with respective double-headed pistons occurs. This lack of lubrication becomes greater when the shoes are engaged with pistons located remote from a return gas inlet through which the refrigerant gas as well as the lubricating oil are introduced into the swash plate chamber of the compressor. Therefore, abrasion of a local portion of the swash plate and the flat faces of the shoes takes place during the operation of the swash plate type compressor due to an insufficient or a lack of lubrication. As a result, inaccurate reciprocating motion of the double-headed pistons, i.e., a lost motion of the pistons due to undesirable play between the pistons and the shoes occurs, and the compressor will generate noise during the operation of the compressor.
Further, in an extreme case, the insufficient or lack of lubrication causes frictional contact between the oblique faces of the swash plate and the flat faces of the respective shoes, resulting in the generation of a high temperature friction heat which cause a seizing of the contacting faces of the swash plate and the shoes, thus reducing the operational life of the compressor.